FOOD SAFETY
Only a few days after Prabhakara Choudary demonstrated his new test for E. coli bacteria, a contamination scare linked to Odwalla juices underscored the importance of having a quick, reliable method for detecting the potentially deadly strain of bacteria.
Choudary, director of the UC Davis Antibody Engineering Laboratory, developed a test that targets a bacterium known as E. coli 0157:H7--the bacterium suspected of sickening at least 49 people who drank the natural juices this fall. In 1993 it caused the deaths of four children who ate undercooked hamburgers from a fast-food restaurant in the Pacific Northwest. In recent months, the same food-borne bacterium has sickened more than 9,000 people in Japan, causing 11 deaths.
Choudary hopes the test will eventually be used by food inspectors and processors to prevent food poisoning caused by the bacteria. Choudary, a molecular biologist credited with several accomplishments in recombinant DNA technology, and Christopher Gooding (shown here), a postgraduate researcher in the Antibody Engineering Laboratory, created the new test together. They developed it for milk, ice cream and meat and are tailoring it for use in seafood. It can probably be adapted to test juices and other foods, Choudary said.
Current procedures used for detecting bacterial contamination in food products typically require at least two days to yield conclusive results. The new test can detect in just eight hours even one cell of the disease-causing bacteria from a sample of a food product.
The test begins with the addition of magnetized beads no larger than the point of a pin to a food sample. The beads have been coated with antibodies--proteins designed to latch on to other specific proteins located on the surface of E. coli 0157:H7 cells. When mixed into the vial of each food sample, the antibody-coated magnetic beads grab hold of the targeted bacteria. A magnet is then placed next to the vial, pulling the beads and their captive bacteria to the side, while the remainder of the food sample is washed out of the vial. The researchers then put each sample of captured bacteria through a process that allows them to make millions of copies of specific segments of the DNA, which can then be analyzed to determine if they contain genes from the bacterium in question.
Photo by Aaron Burg/Latent Image.
